1. Field of the Invention
The present invention relates to a liquid crystal display device and in particular, to a liquid crystal display device and a driving method for controlling the transmittance of the liquid crystal to display a color image.
2. Discussion of the Related Art
A liquid crystal display device includes a liquid crystal panel and a driving circuit panel. The liquid crystal display device controls the quantity of light which penetrate a liquid crystal panel. A backlight provides the light. The liquid crystal panel includes a plurality of pixels arranged in a matrix and a plurality of thin film transistors. The thin film transistors switch data signals which are supplied to each of the pixels.
The liquid crystal panel may include one of two types of color filters. One type includes color filters of R, G and B, and the other type is color filters of cyan and yellow. The liquid crystal display device, which includes the liquid crystal panel with the color filters of cyan and yellow, may display images having four colors.
FIG. 1 is a block diagram illustrating a liquid crystal display device 5 having a liquid crystal display panel with two color filters of cyan and yellow in the related art. In FIG. 1, the liquid crystal display device 5 includes the liquid crystal panel 2 having two kind color filters, a gate driver 4, a data driver 6, a backlight unit 7 and a timing controller 8. The gate driver 4 and the data driver 6 drive the liquid crystal panel 2. The backlight unit 7 irradiates light to the liquid crystal panel 2. The timing controller 8 operates to control the backlight unit 7, the gate driver 4 and the data driver 6. The timing controller 8 divides a frame into two sub-frames, i.e. a first sub-frame and a second sub-frame.
The liquid crystal panel 2 is provided with a first color filter of cyan 3A and a second color filter of yellow 3B. The first and second color filters 3A and 3B form a color filter (not illustrated) as they are arranged repeatedly in the vertical and horizontal directions. Accordingly, each of the color pixels includes cyan sub-pixels and yellow sub-pixels in the liquid crystal panel of the two kind color filters. The liquid crystal panel 2 having the first and the second color filters 3A and 3B displays color images as the quantity of the penetration of four kind color lights is controlled. The four color lights are irradiated alternately from the backlight unit 7 by using two color lights. The backlight unit 7 includes a first LED array 10 having red light emitting diodes 10A producing red light and blue light emitting diodes 10B producing blue light; and a second LED array 11 having green light emitting diodes 11A producing green light and cyan light emitting diodes 11B producing cyan light. The first LED array 10 emits light during the first sub-frame (for example, an odd-numbered sub-frame), and the second LED array 11 irradiates light during the second sub-frame (for example, an even-numbered sub-frame). The backlight unit 7 alternately switches the first and second LED arrays 10, 11 of each sub-frame under the control of the timing controller 8. In this way, one color image is displayed on the liquid crystal panel 2 based on the penetration quantity of the red and blue lights and the green and cyan lights. The red and blue lights are irradiated to the liquid crystal panel 2 from the first LED array 10 during the first sub-frame and the green and cyan lights are irradiated to the liquid crystal panel 2 from the second LED array 11 during the second sub-frame.
The timing controller 8 controls the gate driver 4 and the data driver 6, and controls the sub-pixel drive signals that are supplied to the cyan and yellow sub-pixels. The cyan and yellow sub-pixels form each of the color pixels of the liquid crystal panel 2 one by one during the first and second sub-frames of the first frame period. Simultaneously, the timing controller 8 controls each of the red and blue lights and the cyan and green lights to be irradiated to the liquid crystal panel 2 one by one in turns in accordance with the first and the second sub-frame during the first frame period. Accordingly, the liquid crystal panel 2 displays one color image corresponding to the video data during one frame.
FIG. 2 illustrates the frame divided into the first sub-frame and the second sub-frame. The timing controller 8 divides the single frame period into the first and second sub-frames. Accordingly, each of the first and the second sub-frames corresponds to the half of the frame period. By way of example, the single frame period is 16.67 ms, and each of the first and the second sub-frames becomes 8.34 ms.
For each of the first and the second sub-frames, the sub-pixel drive signals are written one at a time on all of the cyan and yellow sub-pixels of the liquid crystal panel 2. The difference between the sub-pixel drive signal during the first sub-frame period and the sub-pixel drive signal during the second sub-frame period may be gamma characteristics due to different color composition. The difference in the gamma characteristics of the sub-pixel drive signals may affect color reproduction rate of image corresponding to video data.
Each of the first and second sub-frame periods is divided into the data write period AP, the liquid crystal response period WP and the backlight light-emitting period FP. On the other hand, liquid crystal cells mainly forming the sub-pixel in the liquid crystal panel 2 have the same response speed throughout the liquid crystal panel 2. When light emitted from the backlight unit 7 reaches the liquid crystal panel 2, the liquid crystal cells at the upper end area of the liquid crystal panel 2 may be arranged in a state corresponding to the voltage of the respective sub-pixel drive signal, while the liquid crystal cells at the lower end area may not be arranged in a state corresponding to the voltage of the respective sub-pixel drive signal. Accordingly, an image of unintended brightness and color may be displayed on the lower end area of the liquid crystal panel 2.
The unevenness of brightness and colors may be caused by the limited response speed in the liquid crystal display device of two kind color filters. Furthermore, the color reproduction rate of images may be lowered because of the difference in the gamma characteristic between the sub-pixel drive signals of the two sub-frames. The image quality displayed by the liquid crystal display device of two kind color filters may be lowered. Accordingly, there is a need for a liquid crystal display device and a driving method that overcome drawbacks of the related art.